1. Field of the Invention
This invention relates to a catalyst support which has a unique promoter oxide gradient distribution and which can be made into an auto exhaust catalyst.
2. Description of the Previously Published Art
U.S. Pat. No. 4,591,580 to G. Kim and M. V. Ernest discloses stabilized and doubly promoted auto exhaust catalysts. The alumina is stabilized with lanthana and then ceria (CeO.sub.2) is added as one of the promoters in an amount of 1 to 20 wt %. The ceria is applied by spraying with a cerium salt such as cerium nitrate. Although the noble metals are applied with special metal concentration profiles, the ceria and second promoter are not applied with any unique profile.
Toyota Japanese Publication No. 01-56145 published Mar. 3, 1989, discloses a monolithic catalyst which has two ceria concentrations. At the opening end (i.e. the upstream end of the gas flow) the ceria concentration is 0.3-1.0 mol/l and in the downstream section the ceria concentration is less than 0.3 mol/l. The high ceria concentration at the beginning serves to store oxygen so that variances of exhaust gas makeup can be made nearly equal to that of theoretical air and fuel ratio. The downstream section has less ceria so the metal catalyst has ideal conditions to react with the exhaust gas. That disclosure is only pertinent to a monolith structure which has an upstream portion and a downstream portion.
Toyo Kogyo Japanese Publication No. 63-258648 published Oct. 26, 1988, discloses an auto exhaust catalyst where a honeycomb support of cordierite is immersed in two difference ceria solutions. The inlet end has the higher ceria concentration than the outlet end. The purpose of changing the ceria concentration from the level at the inlet end to the level at the outlet end is to have a uniform temperature distribution. Here again, this strategy is only effective for monoliths.
3. Objects of the Invention
It is an objection of this invention to improve the catalytic activity of supported noble metal catalysts.
It is a further object of this invention to improve the mechanical and catalytic durability of supported noble metal catalysts.
It is a further object of this invention to decrease the raw material usage and resulting costs of supported noble metal catalyst.
It is a further object of this invention to maintain existing activity and durability of supported noble metal catalysts by establishing a controlled gradient of catalytic promoter in the catalyst support.
It is a further object of this invention to produce a catalyst support having a promoter oxide and preferably a ceria gradient such that there is a large concentration of ceria at the outer region of the support such as sphere and a significantly lower concentration of the promoter oxide (e.g. ceria) in deeper positions within the sphere.
It is a further object of this invention to provide a support such as a sphere comprising a ceria gradient coupled with a controlled gradient of the noble metals will result in an improved catalyst.
It is a further object of this invention to provide a support such as a sphere comprising a ceria gradient which will result in a vastly improved attrition resistant catalyst.
These and further objects will become apparent as the description of the invention proceeds.